For example, there is a liquid crystal display device having liquid crystals sandwiched between two substrates. There is an organic light emitting display device having an organic light emitting layer sealed between two substrates. In such display devices, a display layer such as a liquid crystal layer and an organic light emitting layer is sealed with a sealant. However, water or the like externally enters the display layer to sometimes cause display unevenness. Display unevenness degrades the reliability of display devices.